1. Field of the Invention
The present invention relates to a backlight module and a display device comprising the backlight module, and particularly to a backlight module, a display device comprising the same with an improved color gamut, and a method of improving the color gamut of the display device.
2. Description of the Prior Art
Due to the popularity of LCD TVs, large sized display panels for the next generation are widely and continuously developed. An LCD TV has the advantages of large size, good display qualities, high brightness, and wide view angle. The LCD panel does not emit light per se, and thus, the backlight module for the LCD TV plays an important role.
Conventional light sources for backlight modules comprise cold cathode fluorescent lamps (CCFL), external electrode fluorescent lamps (EEFL), light emitting diodes (LED), field emission devices (FED), and flat lamp plates. Most display products use a CCFL as a backlight. However, due to the limitations of the fluorescent material used in the lamp and the techniques, the display qualities, such as color gamut and full color, for the device using CCFL still need to be optimized.
FIG. 1 shows various graphs for an NTSC TV color gamut, a conventional CCFL backlight color gamut, and a conventional LED backlight color gamut represented using a CIE chromaticity diagram. Pure, saturated spectral colors are mapped to the “horseshoe” shaped periphery of the visible gamut curve 100. The interior of the “horseshoe” contains all mappings of mixtures of colors, such as spectral red with added blue, which becomes magenta, for example. The interior of the horseshoe can also contain mixtures of pure colors with white, such as spectral red with added white, which becomes pink, for example. The overall color area defined by the “horseshoe” curve of visible gamut 100 is the full range of color that the human visual system can perceive. It is desirable to represent as much as possible of this area in a color display to come as close as possible to representing the original scene as it would be perceived by a human observer.
As shown in FIG. 1, the range of the CCFL backlight color gamut 102 is only 73% based on NTSC TV color gamut 104 (as 100%), and is not sufficient to attain a full color expression. The conventional LED backlight color gamut 106 has a relatively large range. However, when the LED is used with a conventional color filter in a liquid crystal display, the color gamut is deteriorated.
FIG. 2 shows a conventional RGB LED spectrum and a conventional color filter spectrum. As shown in FIG. 2, the RGB LED spectrum has narrower peaks than the color filter, such that the color expression for the LED is relatively pure as in comparison with the color filter. With respect to the color filter spectrum, a range of green light wavelengths overlaps with a range of blue light wavelengths in the shorter wavelength section, and thereby the color purity of light emission in this section is further reduced. When such LED is used as a light source in a backlight module, the gamut of the LED together with a color filter is determined to be about 99% of the NTSC TV gamut, in which the red light, green light, and blue light of the LED have a wavelength of 633 nm, 519 nm, and 450 nm, respectively, as shown in FIG. 3. Accordingly, the color saturation is not sufficiently improved simply by replacing CCFL with LED.
Therefore, there is still a need for a novel method to improve color gamut for better color saturation and a display device with improved color saturation.